1. Field of the Invention
The present invention relates to an elastomer composite in which the dispersion of conductive fillers is improved by an ionic liquid, achieving improved dielectric properties, and a method for producing the elastomer composite.
2. Description of the Related Art
Polymers have excellent characteristics in terms of processability, mechanical strength, electrical insulation, optical transparency, mass productivity, etc. compared to other materials. Due to these advantages, polymers are used as important new materials in high-technology industrial applications, including semiconductors, electrical/electronic industry, aerospace, defense industry, displays and alternative energy. The advantages of polymeric materials as dielectric materials are various physical properties obtainable by molecular design and excellent moldability. However, polymeric materials have the disadvantages of poor thermal and mechanical properties over inorganic materials as well as poor dielectric properties. These disadvantages greatly limit the application of polymeric materials to new materials.
Polymers are currently being investigated to utilize their dielectric properties in high-κ gate dielectrics for flexible electronic materials, capacitors for energy storage, and dielectric elastomer actuators (DEAs).
High dielectric constant polymeric materials in single phases are free from problems associated with the dispersion of multi-phase materials, thus being ideal for use in embedded capacitors. In recent years, a research team from the University of Pennsylvania has reported a method for preparing an electroactive PVDF polymer having a dielectric constant of 100 by exposing a PVDF copolymer film to radiation, followed by electric field poling. Shizuoka University, Japan, has achieved a dielectric constant of 20 or above using a polymer having polar cyano groups. Further, the German Plastic Institute and the University of Wales, UK, have prepared polymer dielectrics with a dielectric constant of 8 or above using PVDF and relevant copolymers. However, they suffer from problems of high cost, low yield and suitability for subsequent processing, limiting their application to the manufacture of large-area embedded capacitors.
Dielectric elastomer actuators based on electroactive polymers (EAPs) feature the ability to mimic the movement of human muscles. This feature has motivated research aimed at applying dielectric elastomer actuators to the development of artificial muscles.
Electroactive polymers, i.e. elastomers, refer to materials that undergo deformation in response to a voltage or force applied thereto. Electroactive polymers have the ability to convert such an electrical force to a mechanical strain and can be applied to dielectric elastomer actuators. However, since elastomers have relatively low dielectric constants, the application of high operating voltages is inevitable for actuation behavior. Thus, attempts to increase the dielectric constant of elastomers for the purpose of lowering high operating voltages applied to the elastomers are needed to increase the commercial viability of dielectric elastomer actuators using the elastomers and to reduce risks accompanied by the application of the high voltages.
To solve such problems, research has been conducted recently to increase the dielectric constant of elastomers by compounding high-κ fillers with the elastomers. For example, Japanese Unexamined Patent Publication Nos. 2008-239929 and 2005-177003 disclose that the addition of lithium-containing ceramic fillers to thermoplastic elastomers increases the dielectric constants of the elastomers at low cost to achieve improved electrodynamic conversion efficiency. PCT International Publication No. WO 98/04045 discloses an actuator using a composite produced by adding conductive fillers, such as carbon black, graphite or metal particles, to an elastomer. Investigations into the dispersion of one-dimensional, high aspect ratio conductive fillers, such as carbon nanotubes, in elastomers to ensure high dielectric constants of the elastomers are being conducted by some groups. However, the dielectric constant and dielectric loss of such an insulator/conductor composite increase simultaneously with increasing amount of the conductors filled. The increased dielectric loss of the composite leads to a drop in the dielectric strength of the elastomer. This phenomenon causes a dielectric breakdown in the elastomer even at a low voltage to substantially limit the application of the elastomer. In attempts to solve such problems, studies are currently underway to lower the dielectric loss of elastomer composites by using chemically or physically surface-modified carbon nanotubes.